The present invention generally relates to isolation groove structures and methods for production thereof, and more particularly to isolation groove structures in which a deep isolation groove has a cross section with substantially straight and parallel side wall portions and a generally V-shaped bottom portion and a shallow isolation groove has a generally V-shaped cross section, and to a method for producing such isolation groove structures.
Techniques for isolating elements were developed when integrated circuits came into existence. At first, the junction isolation technique was used to isolate the elements, but with such technique the reduction of the element isolation region limited due to the lateral diffusion of the junction isolation. For this reason, the dielectric isolation technique was developed as the integration density of integrated circuit improved.
Dielectric isolation procedures such as the LOCOS process and the isoplanar isolation process are popularly used because with such procedures it is relatively easy to form oxide isolation layers. However, there is a problem in that the oxide layer obtained by the selectively oxidized isolation process are too wide. The isolation groove structure was developed to further improve the integration density of the integrated circuit.
The isolation grooves of the isolation groove structure may be classified as isolation grooves having a generally U-shaped cross section and isolation grooves having a generally V-shaped cross section. In the present specification, isolation grooves having a generally U-shaped cross section will be referred to as an U-grooves, and isolation grooves having a generally V-shaped cross section will be referred to as a V-grooves.
U-grooves are especially suited for the case where the isolation groove needs to be narrow and deep. However, when forming a U-groove, the are problems in that etching residue may remain at the bottom of the U-groove and the U-groove may not have a cross section with substantially straight and parallel side walls.Hence, when the U-groove is oxidized, the oxide layer is not uniformly formed at the portions of the U-groove where the shape irregularities exist. Furthermore, when a filling material such as polysilicon is subsequently introduced into the oxidized U-groove, the polysilicon does not completely fill the inside of the U-groove and portions thereof remain unfilled by the polysilicon. As a result, stresses are generated inside the U-groove. In other words, the generation of crystal defects is facilitated and cracks may be formed in the substrate in extreme cases, as will be described hereinbelow. In addition, when such things occur, it is difficult to control the depth of U-grooves.
On the other hand, it is easy to control the depth of the V-grooves. As will be described later in the specification, when the anisotropic etching characteristics of the 100-oriented silicon are used to form V-grooves, lack resultant V-groove is 0.7 times its width, However, it causes the V-groove. However, in the case where the isolation groove needs to be deep, there is a problem in that the width of the V-groove must consequently be wide. This does not improve the integration density of integrated circuits.
In order to further improve the integration density of integrated circuits, it is desirable to form narrow isolation grooves without generation of stresses as described above. Accordingly, there is need for isolation techniques in which the problems described above are eliminated.